Why was chillingworth called a leech in The Scarlet Letter?

A leech is a hanger-on who seeks advantage or gain. Roger Chillingworth is a perfect example of a leech. He has attached himself to Arthur Dimmesdale like a harmful and vicious worm. His only goal in life is to expose Dimmesdale's ignominy and get revenge. Once Dimmesdale died Chillingsworth had nothing to attach himself to so he died as well.